The present invention relates to a drive control system for a motor vehicle.
More specifically, the subject of the invention is a drive control system for a motor vehicle, provided with:
an internal combustion engine with associated control means for operating the engine in a manner such that the engine delivers a driving torque which is variable in dependence on predetermined measured parameters, in particular on the position of an accelerator pedal, and
sensor means for providing electrical signals indicative of the position of the accelerator pedal and of the rate of rotation of the shaft of the engine or of the forward speed of the motor vehicle.
WO-A-97 37 868 discloses such a system, in which the accelerator position and the vehicle speed are used to determine, from stored graphs, the value of a correspondingly desired tractive force. The latter is multiplied by the vehicle speed to determine the corresponding value of the required power. At the same time the transmission ratio is shifted to an optimum ratio (if different therefrom), which is determined as a function of the accelerator position and the vehicle speed. The torque to be delivered by the engine is then computed on the basis of both the required power and the optimum transmission ratio.
EP-A-0 559 342 discloses a system for improving the fuel economy of a car equipped with an automatic transmission having a lock-up clutch. The system controls both the engine and the automatic transmission on the basis of a target driving torque corresponding to the stroke of the acceleration pedal.
U.S. Pat. No. 4,353,272 discloses a system for controlling the engine-transmission assembly of a motor-vehicle wherein the position of the accelerator defines the power setpoint of the engine.
According to the prior art, the command imparted by means of the accelerator is interpreted by an engine management unit in accordance with a so-called xe2x80x9cdriveability mapxe2x80x9d which is stored in a memory and which causes a predetermined driving torque delivered by the engine to correspond unequivocally to each position of the accelerator pedal and to each rare of rotation of the engine shaft.
According to the rate of revolution of the engine, the command imparted by the accelerator is thus xe2x80x9ctranslatedxe2x80x9d by the engine management unit directly into a value of the driving torque delivered to the engine shaft. The power or the torque which is actually applied to the driving wheels thus depends not only on the driving torque thus delivered by the engine but also on the transmission ratio put into effect by the gearbox.
The object of the present invention is to provide an innovative drive control system for a motor vehicle which, in particular, enables the engine to be managed with more degrees of freedom than with conventional systems. This and other objects are achieved, according to the invention, by the system the main characteristics of which are defined in appended claim 1.
The control system according to the invention is applicable in particular and advantageously to integrated drive control in a motor vehicle having a servo-assisted gearbox comprising an input shaft which can be coupled to the engine shaft by means of a servo-controlled clutch, and in which first and second electrically-operated actuator means are associated with the gearbox and with the clutch, respectively.
In motor vehicles having servo-assisted or xe2x80x9cautomaticxe2x80x9d gearboxes, drive control, that is, control of the power or torque applied to the driving wheels and exchanged with the ground, is the combined result of the command imparted by the driver by means of the accelerator pedal and of the gear ratio selected by the driver.
In these motor vehicles, if the driver is not particularly skilled, drive control, that is, the torque actually applied to the driving wheels and exchanged with the ground is not generally optimal.
A further object of he present invention is therefore to provide an integrated drive control system which is better than the conventional method of separate control of the engine and of the gearbox, permitting improved and more direct control of the power applied to the driving wheels, greater driving comfort and optimized use of the engine in accordance with predetermined objectives such as a reduction in consumption and/or exhaust emissions.
This and other objects are achieved, according to the invention, by an integrated drive control system the main characteristics of which are defined in appended claim 3.
As will be appreciated better from the following part of the present description, a system of this type according to the invention is based upon the concept of controlling, directly by means of the accelerator pedal, the power which is applied to the driving wheels of the vehicle and not the driving torque delivered by the power unit. In other words, it is not purely and simply the engine which is controlled by the driver means of the accelerator pedal, but rather the dynamics of the forward movement of the vehicle.